Crowdsourcing involves outsourcing some job to a distributed group of people online, typically by breaking the job down into microtasks. Online markets offer human users payment for completing small tasks, or users can participate in nonpaid platforms such as games and volunteer sites. These platforms' general availability has enabled researchers to recruit large numbers of participants for user studies, generate third-party content and assessments, or even build novel user experiences. This special issue provides a snapshot of the most recent crowdsourcing research.